1. Field of the Invention
The present invention relates to a method and an apparatus for monitoring a density profile of impurities. More particularly, the present invention relates to a method and an apparatus for monitoring a density profile of boron (B) or phosphorous (P) in an insulating interlayer of the semiconductor substrate.
2. Description of the Related Art
Technological trends of high integration degree and operation speed of recent semiconductor devices render intervals between various patterns in a memory cell shorter, so that a space between gate electrodes becomes narrower and a conductive pattern forming a gate electrode becomes higher. Therefore, coating an insulating interlayer to planarize a substrate surface frequently causes a void defect between two adjacent gate electrodes.
A borophosphorous silicate glass (hereinafter, referred to as BPSG) is now widely used as an insulating interlayer to prevent a void defect since BPSG has good fluidity and step coverage. The BPSG includes small doses of boron (B) and phosphorous (P) in a silicon oxide (SiO2) layer, and is generally deposited on a substrate surface through an atmospheric pressure chemical vapor deposition (APCVD) process. Accordingly, an operation characteristic of a BPSG layer is decisively influenced by the density of boron (B) and phosphorous (P). More specifically, the density profile of the boron (B) and phosphorous (P) distributed along a depth of a cross sectional surface of a BPSG layer (hereinafter, referred to as “depth profile”) has more effect on operation characteristics of the BPSG layer than does the bulk density of the boron (B) and phosphorous (P).
When relatively small quantities of the boron (B) and phosphorous (P) in a lower portion of the BPSG layer are used, a void defect is more frequently generated and a static refresh rate is considerably reduced during a self-aligned contact process. In addition, an etching rate is strongly influenced by the densities of the boron (B) and phosphorous (P) Therefore, the cross sectional surface of the BPSG layer becomes non-uniform in accordance with the density profiles of the boron (B) and phosphorous (P).
In general, the density profile of boron (B) or phosphorous (P) has been measured by a secondary ion mass spectrometry (SIMS) method or a glow discharge luminescence spectrometry (GDLS) method. However, the SIMS and GDLS methods are carried out after destruction of the BPSG layer. Furthermore, a density analysis method using a Fourier transform infra-red (FT-IR) apparatus indicates the bulk density of boron (B) and phosphorous (P), but does not indicate any information regarding density variation along a thickness of the BPSG layer.
Therefore, there is a need for an improved density analysis method for analyzing a depth profile of boron (B) and phosphorous (P) in real time during the process without destruction the substrate.